In 1935 Erwin Schrodinger proposed a famous thought experiment in which a cat was brought in a coherent quantum state and thereby rendered alive and dead at the same time. Schrodinger used this thought experiment to illustrate conceptual problems in the interpretation of quantum mechanics. In the years thereafter, and in fact throughout the twentieth century, Schrodinger's cat has been subject of various debates and a vast number of scientific studies on the conceptual foundation of quantum mechanics. As a result, Schrodinger's cat has led to alternative interpretations of quantum mechanics, including the many-worlds interpretation.

Also, Schrodinger's cat became a recurring theme in popular culture and continued to amaze and intrigue not only the general public, but also students of quantum physics. Now, three quarters of a century later, a Spanish-German collaboration is proposing real-life Schrodinger cat experiments.

Animal rights activists need not worry (yet). The goal of the proposed experiments does not involve quantum catslaughter. Initial focus is on bringing nano-sized lifeforms such as viruses into quantum superpositions. This in itself would open up the possibility to observe genuine quantum effects with living organisms. However, these experiments need not be limited to nano-sized organisms, but could be extended to bring larger and more complex living organisms to the quantum realm. Organisms sized up to 1 mm could in principle be brought in quantum superposition. Cat-sized animals, and experiments addressing the role of consciousness in quantum mechanics might not be within immediate reach.

Yet, the proposed experiments – when successful - will be a first step towards such a goal.

The proposed experiments build on recent progress in quantum optomechanics, and involve living organisms such as viruses levitating in vacuum inside an electromagnetic cavity. The fact that these organisms will not be in contact with any mechanical objects should enable so-called ground state cooling and would at the same time avoid decoherence of their quantum states.

Viruses are ideally suited for these experiments not only because they have dielectric properties, but also because their size is comparable to the laser wavelengths used in these quantum optomechanics experiments. Furthermore viruses exhibit high resistance to extreme conditions and can live in low-pressure vacuum. As an example, the common influenza viruses, with a typical size of 100 nm, can be stored for several weeks in deep vacuum.

It is believed that the condition of the microorganism being of size comparable to the wavelength of the light used can be relaxed. This would allow extension to objects larger than the wavelength, and would permit us to bring larger and more complex living organisms to the quantum realm. For instance, the Tardigrade or water bear, with size ranging from 100 μm to about 1.5 mm, is known to survive during several days in open space.

One would assume that in the proposed quantum optomechanic experiments it will not die, but get into a quantum superposition of life and death.

Comments

Maybe I'm missing something, but concepts like quantum immortality sound suspiciously like Zeno's paradoxes regarding the flight of an arrow and the halving of distances (Achilles&the Tortoise).

In addition, how does one determine the superposition of life and death? After all, if one were to attempt any determination, it would fix the final state. So how does that translate into anything other than the normal probability of surviving or dying? I would also be curious to know if the resulting virus is identical to the original one, or if a state like superposition could actually modify the organization of the underlying molecules (in other words, does the quantum state of each particle maintain uniformity, or is it subject to individual results)?

The proposed experiment forces us to face fundamental questions like "what does it mean when a life being is in a pure quantum state?". This is a field of active research (or should I say active speculation?). According to a recent paper, a life being that is in a coherent superposition of quantum states would not undergo a single experience. Yet an external observer would be able to demonstrate the subject is in a superposition of awareness states. Such a superposition can be demonstrated by the external observer by executing quantum interference experiments. This is akin to the interference effects of an electron in a double slit experiment. A subject in a coherent superposition of 'life' and 'death' would similarly show interference effects between both states.

Quantum immortality is a speculation. A speculation relying on the many-worlds interpretation of quantum mechanics. The amplitude (and thereby the likelihood) of survival keeps decreasing, yet anthropic considerations do play a role, and I would not classify quantum immortality as an example of Zeno's paradox. Personally, I believe quantum immortality is a gedanken artifact that demonstrates we are still wrestling with classical interpretations of quantum mechanics that are linked with our non-quantum experience and intuition of the world around us.

Finally, ground state cooling would not alter the molecular configuration (chemical bonds) of the object. Just think about it as an 'ultra deep freeze' combined with a perfect isolation from the environment.

Yet an external observer would be able to demonstrate the subject is in a superposition of awareness states. Such a superposition can be demonstrated by the external observer by executing quantum interference experiments. This is akin to the interference effects of an electron in a double slit experiment. A subject in a coherent superposition of 'life' and 'death' would similarly show interference effects between both states.

In the double slit experiment, you either collapse the wave with a single detector behind either slit or you perceive the full range and thus collapse in an interference pattern.

So i fail to see where in your analogy you can discern an external observer, which is not collapsing the superposition.
I thought the interference pattern meant you collapsed the wave along the complete projection path.
Am i incorrect in this assumption ?

According to a recent paper, a life being that is in a coherent superposition of quantum states would not undergo a single experience.

Maybe I'm being dense, but instead of a superposition of states, couldn't this simply be described as being in "no state since time has stopped" until an event occurs that forces a direction? In other words, if events or interactions (experiences) do not occur, then effectively time has ceased to exist. So it would suggest that the object isn't so much in a superposition of states, as it is in "no state" until time restarts.

Finally, ground state cooling would not alter the molecular configuration (chemical bonds) of the object.

Actually my question in this regard is more concerned with the state of each particle in such an organism. Since (at least to my understanding), each particle of the whole should be in a superposition state which implies that each particle may undergo its own changes instead of being locked into the behavior of the whole. Am I missing something here? In other words, does the use of a larger object necessarily require that all the quantum states of the individual particles are now committed to each other, so that they change in a uniform fashion? If not, then my question remains because it would suggest that molecular bonds coming into the experiment might not be the same as coming out.

"couldn't this simply be described as being in "no state since time has stopped" until an event occurs that forces a direction?"

Suppose the life being is in a superposition of awareness states A and B. According to the paper quoted, the life being would build "parallel" experiences A and B. However, if at the end of the experiment upon measurement the state of awareness would collapse to B, the life being would remember B but would not be able to remember A.

"Actually my question in this regard is more concerned with the state of each particle in such an organism."

Not sure if I understand the issue you see. Each degree of freedom of the life being (every molecular mode of movement) would be in one uniform state.

However, if at the end of the experiment upon measurement the state of
awareness would collapse to B, the life being would remember B but
would not be able to remember A.

While I understand what the paper is claiming, I'm not sure how that works in a real biological system. After all, it would seem that the act of "experiencing" anything would be tantamount to a measurement and cause a collapse. Secondly, the act of being aware and then being unable to remember requires that neuron states be modified and changed once a collapse occurs, so I'm not sure how that translates between the quantum expectation and the biological reality of the organism involved.

"I'm not sure how that works in a real biological system"I'd be surprised if anyone is. That's why the proposed direction of experiments is indeed interesting.

Let's compare two experiments:

1) a life being is brought in a coherent quantum superposition of awareness states 'A' and 'B', and subjected to a measurement of its 'state of awareness' which results in the state of awareness 'A'. Next, the memory state of the life being is measured.

2) a life being is in state of awareness 'A' and then subjected to a measurement of its state of awareness (which obviously results in outcome 'A'). Next, the memory state of the life being is measured.

Are you suggesting that 1) and 2) would lead to two different results on the memory of the life being?

I'm confused about your use of the term "awareness". For example, if we assume something simple like experiencing whether the subject sees a red light or green light. A superposition of experiences suggests that the subject sees both red light and green light. Once the memory state is measured, they would only have a memory of one or the other.

However, from a biological perspective, we're talking about two interpretations that the brain must store. To "experience" both phenomenon says that photons have interacted with the retina producing a specific brain sensation. Therefore to conclude with only the memory of one event, suggests that the memory of the "other" must have been reversed or erased.

I'm not clear on how any of these events can occur without them causing a collapse of the function and becoming one or the other. In other words, it seems that biological systems by having an experience, by definition, result in a measurement (or interaction) that would preclude maintaining a superposition.

My problem comes from the term "awareness". This isn't a specific state, but is a continuous process in living organisms. When I look at an object it isn't a one-time fixed event. It is a continuous interacting stream of photons that creates my awareness.

Therefore to talk about a superposition of awareness states is confusing to me.

It sounds like what is being suggested is that the living organism does NOT have a state of awareness, but rather is in superposition with two potential states of awareness which resolve to one. In other words, the "awareness" is actually suspended until the event is resolved.

Gerhard -- it think I understand your concerns, but would like to check this assumption and at the same time try to clarify matters.Suppose in your comment I change the word 'awareness' into 'path taken' and 'living organism' into 'electron in a double slit experiment', etc. We then get the following comment:

My problem comes from the term "path taken". This isn't a specific
state, but is a continuous process for an electron in a double slit experiment. When an electron takes a certain path, it isn't a one-time fixed event. It is a continuous
interacting stream of positions that creates its path.

Therefore to talk about a superposition of paths is confusing to me.

It sounds like what is being suggested is that an electron does
NOT follow a path, but rather is in superposition of two paths which resolve to one. In other words,
the "path" is actually suspended until the electron is detected.

Would you agree with this comment?

If so, I can assure you that the correct interpretation is that an electron (and all quantum systems) do not follow a specific history (or path), but explore a coherent superposition of paths. There is tons of hard experimental evidence for this. Quantum systems are know to undergo a 'collapse' into a specific history in delayed choice experiments.

It all may sound vague (and actually as stated it is incredibly vague and imprecise), but the problem is that our intuition is simply not used to quantum behavior.

Thank you, you've expressed it exactly. So, to extend the point back to my question....I understand the double-slit experiment and our intuition. However, an electron doesn't have a "memory" to forget what it did. There is no interaction until a measurement occurs, so the electron is essentially in a "suspended" state.

However, my point is that in a living organism, the concept of "awareness" already suggests an interaction with the environment that cannot both simultaneously exist and not yet be determined. While I understand that effect on an electron, it makes no sense in a living organism, since the organism must have an interaction in order to register the awareness. Therefore, once it is "aware" how can that state be undone?

It would be like the electron was measured as traveling through both slits and then saying that there is no history of it having traveled through one of them. Specifically, isn't "awareness" a type of measurement?

It would be like the electron was measured as traveling
through both slits and then saying that there is no history of it
having traveled through one of them. Specifically, isn't "awareness" a
type of measurement?

That is exactly what happens in the double slit experiment. If electrons are fired one-by-one and hit the screen such that an interference pattern builds, each electron is confirmed to have traveled through both slits. (I they would all have selected one slit, no interference would have been observed.) Yet there is no history for any of the electrons having traveled through one of them. In this context, the question "which slit did it pass?" can be labeled as invalid, as this is asking for a value of an 'unobservable.

In 'awareness superposition scenarios', we also have to ask ourselves "what are the observables?" Do you agree with the statement that in such a context memory is an observable, whilst awareness isn't?

Do you agree with the statement that in such a context memory is an observable, whilst awareness isn't?

I guess that's where I get stuck. Perhaps I'm just too hung up on the physiological elements of what I consider memory and awareness to be. In the double-slit experiment we are only asking one specific question and anticipating one specific interaction. Did the electron travel through one slit or both. We are concluding based on the pattern which emerges which one of our scenarios is true. If we attempt specifically to measure which slit, then we determine the outcome by that measurement, so it isn't really true to say that we know how it works, but rather we surmise what must have happened from the pattern which emerges.

So when we talk about awareness of memory, I'm thinking of the numerous interactions that need to occur in order to translate the event from the external world in the brain of the subject. These actions require definitive states to exist in order for a memory to be created. For example, a photon interacts with the retina of the eye, which causes a signal sent along the optic nerve to the brain, which triggers neurons to respond, which stores it in short-term memory, etc. So if we consider someone experiencing the sensation of seeing a red light and a green light, the superposition state suggests that both experiences are present.

So my question comes in where, if these activities occur for two simultaneously opposite events (during the superposition), then it suggests that we have to "undo" something to eliminate the memory, rather than that we are simply surmising what has occurred by only recollecting one of the events. In other words, how do we "undo" the memory of the red or green light?

So my question comes in where, if these activities occur for two
simultaneously opposite events (during the superposition), then it
suggests that we have to "undo" something to eliminate the memory,
rather than that we are simply surmising what has occurred by only
recollecting one of the events. In other words, how do we "undo" the
memory of the red or green light?